No. The deposit and reservation are paid directly to the hotel. SXSW Housing & Travel simply facilitates the booking. Nothing is charged at the time of booking, but a valid credit card is required to secure your reservation.
Most SXSW properties charge an advance deposit to your credit card when they receive and assign your reservation confirmation number in late February. The deposit amount depends on the hotel you booked and is detailed in the Reservation Agreement section of your reservation confirmation email.
You can also view deposit information prior to booking in the "See All Amenities" section for each hotel on the Availability Page. Note that some hotels do not require an advance deposit.
All reservations are paid to the hotel directly upon check-out. If you do not intend to travel with the credit card you plan to use to pay for the reservation, you must submit a credit card authorization form to the hotel before you arrive. This allows you to charge your reservation, tax and, if you choose, incidentals to a card that is not in your name (i.e. a company card that does not belong to the employee).